Poly arylene ethers are tough, rigid, flame-retardant engineering thermoplastics with high glass transition temperatures. Consequently, these materials are well suited to optical applications. These polymers also display better resistance to basic environments than do other higher temperature thermoplastics such as polyimides.
Poly ether phosphine oxides are particularly well suited for optical applications because of their high refractive indices. PEPOs are amorphous polymers due to the presence of flexible ether linkages in the polymer backbone and large phenyl groups pendant to the phosphorus. These features increase the solubility of PEPOs in many common solvents.
Although the melt synthesis of poly(arylene ethers) has been described, PEPOs have been synthesized in solution by either a strong base route or a weak base route. For example, UDEL.RTM. (Amoco), a polyether sulfone, has been synthesized by the strong base route by Johnson et al., J. Polymer Sci, Part A-1, 5, 2375 (1976). Riley et al., Polym. Eng. Sci. 37, 1507-1511 (1997), describes the synthesis of PEPOs by the weak base route. This method results in products with impurities, the removal of which requires additional purification steps.
Synthesis of PEPOs by a solution method can require about twenty hours to obtain a polymer of 30,000 g/mole. Insoluble salt by-product of the weak base route, such as, potassium fluoride, must be filtered out before the polymer is precipitated. Residual salt that is left in the polymer can have a detrimental effect on the transparency of films by causing haze.
The solvents used in solution methods are another source of contamination because of degradation and side reactions at temperatures above about 150.degree. C. If amide solvents, such as, N, N-dimethylacetamide and N-methylpyrrolidinone, which are used in solution synthesis can be avoided, non-yellowing properties of the polymer will be enhanced. Solvents are a further concern because of their potential environmental impact and the hazards of handling flammable materials.